Molecular imaging has great promise for improving diagnosis and treatment of patients with various diseases. For example, PET/CT (PET—Positron Emission Tomography combined with CT Computerized Tomography scans utilizing injections of F-18 labeled tracer molecules to detect minute anomalies in the patients tissues. To assess the patient's response to treatment or predict whether a particular tumor will respond to a particular treatment, quantifying the behavior of the tissues, diseases, biological, or physiological under study could be necessary. Quantification is currently done in several ways:
In the standard uptake value (SUV) method, the tracer imaged in a tissue is normalized by the dose given and some patient characteristic, such as weight, lean body mass, or body surface area. However, SUV changes with the time between injection and image acquisition for different tumors.
Methods in which the patient is injected on the PET scanner and a series of images are acquired for 10 or 20 minutes and then 55 to 60 minutes post injection have provided some improvement over SUV. However, patient body position re-registration and patient waiting time between scans and logistics of rescanning pose problems with these methods. Acceptable results (80% correlation) have also been obtained using a 16 minute dynamic scan.
Thirty and 40 minute scans have been used to produce a model of the forward and reverse transport of FDG between the blood and tissue. However, these methods may be sensitive to the early phases of time-activity curves of tumor and input function.
Methods such as the Patlak plot, the Sokolof method, and the Logan Plot acquire PK/PD (pharmacokinetic/pharmacodynamic) by injecting the patient in the PET/CT scanner and acquiring images over a length of time. Models associated with these methods can calculate, estimate, or infer quantities such as tissue perfusion, blood vessel permeability, tissue glucose metabolism, and the presence of hypoxia. However, this often requires that the patient be in the scanner for 60 or 90 minutes.